"The safety of MMR vaccination has been questioned because disease flares have been described after MMR vaccination," wrote Dr. Marloes Heijstek, of the University Medical Center Utrecht in the Netherlands, and colleagues. "Our trial does not show an effect of vaccination on [juvenile arthritis] activity."

The study included 137 juvenile arthritis patients, aged 4 to 9, who had received primary MMR vaccinations and were randomly assigned either to receive an MMR booster shot or not receive a booster. During follow-up, juvenile arthritis disease activity was about the same for both groups, according to the study, which was published in the June 19 issue of the Journal of the American Medical Association.

The average number of disease flares per patient was 0.44 in the booster shot group and 0.34 in the non-booster group, and both groups had a similar percentage of patients with one or more flares.

Juvenile arthritis is the most common childhood rheumatic disease, and affects between 16 and 150 children per 100,000. Patients with juvenile arthritis are at increased risk for infections due to weakened immune systems caused by the disease or its treatment. Preventing infections in these patients requires safe and effective vaccinations that do not increase disease activity, the researchers noted in a journal news release.